II. Indication

  1. Suspected Pulmonary Embolism

III. Approach

  1. Determine PE Probability (Low, Moderate, High)
    1. High Sensitivity (Negative Scan almost excludes PE)
    2. Low Specificity (Positive Scan does not confirm PE)
  2. Radiologist interprets scan
    1. Two medium to large perfusion defects on V/Q mismatch
      1. Probability of PE: 90%
    2. One medium to large perfusion defect on V/Q mismatch
      1. Probability of PE: 50%
    3. Small perfusion defects
      1. Probability of PE: Low
  3. Complete by combining Clinical and Radiographic data
    1. Concordant Reading
      1. Low suspicion and Normal scan: 4% Incidence PE
      2. High suspicion and High scan: 96% Incidence PE
    2. Discordant Reading: Further workup required
      1. Only 40% of PE patients have High scan
      2. As many as 12% of PE patients have Low scan

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